The commercial production of sodium bicarbonate generally begins with the mining of trona ore, which is processed in “soda” plants to produce sodium carbonate. The desired product of that production is a high quality and fairly pure sodium carbonate product. In normal sodium bicarbonate production the pure sodium carbonate product is then converted to sodium bicarbonate in a separate plant. The conversion of the carbonate to bicarbonate is typically done in a “no waste-water effluent” manner.
The actual mining of trona ore may be accomplished by either dry mining or solution mining. Following dry mining, the trona ore is conventionally processed according to either the sesquicarbonate process or the monocarbonate process. The sesquicarbonate process involves a series of steps, including: dissolving crude mined trona in a cycling, hot mother liquor containing excess normal sodium carbonate over sodium bicarbonate in order to dissolve the trona congruently, clarifying the insoluble muds from the solution, filtering the solution, passing the filtrate to a series of vacuum crystallizers where water is evaporated and the solution is cooled causing sodium sesquicarbonate to crystallize out of the solution in a stable crystal phase, recycling the mother liquor to dissolve more crude trona and calcining the sesquicarbonate crystals at a temperature sufficient to convert same to sodium carbonate, or soda ash.
A more direct and simplified method developed subsequently to the sesquicarbonate process is the monohydrate process. The monohydrate process tends to yield a dense, organic-free sodium carbonate product through a series of steps which include: calcining the crude trona ore at a temperature of about 125 degrees C. to about 500 C. to convert the trona ore to crude sodium carbonate and to reduce the amount of the organics by oxidation and distillation, dissolving the crude sodium carbonate in water, clarifying the resulting sodium carbonate solution to remove insoluables as muds therfrom, filtering the clarified solution, evaporating water from the clarified and filtered sodium carbonate solution in an evaporator circuit, crystallizing sodium monohydrate crystals from the pregnant mother liquor, calcining the monohydrate crystals to produce a dense, organic-free sodium carbonate product and recycling the mother liquor from the crystals to the evaporation step. The dense soda ash product produced by the monohydrate process has become has become the standard product of the trona based sodium carbonate/soda ash industry.
Still another trona processing technology involves solution mining. Solution mining has become of more interest as costs associated with dry mining have increased. Futhermore, solution mining offers a process by which the large quantities of ore remaining as pillars, walls, and ceilings in previously dry mined areas may be recovered. In its simplest form, solution mining involves dissolving trona ore into a solution and recovering sodium products from the solution. For example, a trona ore deposit, or other sodium-containing ore, is contacted with a solvent, such as water. The water dissolves the trona ore creating a brine. The brine is recovered and processed to recover sodium carbonate, sodium bicarbonate, sodium sesquicarbonate, sodium monohydrate, or other sodium products. The sodium depleted brine is typically recycled to the trona ore deposit to dissolve additional trona.
Over the years, commercial waste-water production has been severely curtailed by governmental action. First, water use demand needs to be kept low in commercial processes (where possible) so as to allow for adequate supplies for personal use and for commercial use that cannot be further reduced. Second, effluent water must be treated before being released into the environment so as to have as little an impact on the environment as possible. Unfortunately, waste-water treatment facilities are limited by both the volume of waste-water they can handle and the contaminants which might be in the waste-water. For these reasons, there has been severe governmental pressures to keep the volume of waste-water from commercial facilities to as low an amount as possible. In this vein, the amount of waste-water which can be discharged by a commercial plant is heavily regulated and subject to governmental permits.
Therefore, processes that allow for a reduction of effluent waste-water over current commercial production processes are highly sought after.
In addition, as non-renewable natural resources, such as mined ore, are used, there becomes an ever increasing need to extract more and more desired product from the production line using the same amount of starting ore. It would be highly desired to recover any significant amount of additional product without having to mine additional ore.
To achieve both additional production of desired product and simultaneously reduce effluent waste-water is a truly prized situation that is desired in any commercial process. Achieving these typically requires a trade-off in reduced product purity; to achieve these with improved product purity would obviously be the best possible result.